1. Field of the Invention
This invention relates in general to disk drives, and in particular to limit stops in the disk drives whose function is to limit the extent of actuator radial motion, to define the usable radius of the disk surfaces and to protect the suspension and slider from damage due to contact with the disk stack hub at the inner diameter of the disk or due to running off the disk surface at the outer diameter of the disk.
2. Description of Related Art
Moving magnetic storage devices, especially magnetic disk drives, are the memory devices of choice. This is due to their expanded non-volatile memory storage capability combined with a relatively low cost.
Magnetic disk drives are information storage devices which utilize at least one rotatable magnetic media disk having concentric data tracks defined for storing data, a magnetic recording head or transducer for reading data from and/or writing data to the various data tracks, a slider for supporting the transducer in proximity to the data tracks typically in a flying mode above the storage media, a suspension assembly for resiliently supporting the slider and the transducer over the data tracks, and a positioning actuator coupled to the transducer/slider/suspension combination for moving the transducer across the media to the desired data track and maintaining the transducer over the data track center line during a read or a write operation. The transducer is attached to or is formed integrally with the slider which supports the transducer above the data surface of the storage disk by a cushion of air, referred to as an air-bearing, generated by the rotating disk.
Alternatively, the transducer may operate in contact with the surface of the disk. Thus the suspension provides desired slider loading and dimensional stability between the slider and an actuator arm which couples the transducer/slider/suspension assembly to the actuator. The actuator positions the transducer over the correct track according to the data desired on a read operation or to the correct track for placement of the data during a write operation. The actuator is controlled to position the transducer over the desired data track by shifting the combination assembly across the surface of the disk in a direction generally transverse to the data tracks. The actuator may include a single arm extending from a pivot point, or alternatively a plurality of arms arranged in a comb-like fashion extending from a pivot point. A rotary voice coil motor (vcm) is attached to the rear portion of the actuator arm or arms to power movement of the actuator over the disks.
The vcm located at the rear portion of the actuator arm is comprised of a top plate spaced above a bottom plate with a magnet or pair of magnets therebetween. The vcm further includes an electrically conductive coil disposed within the rearward extension of the actuator arm and between the top and bottom plates, while overlying the magnet in a plane parallel to the magnet. In operation, current passes through the coil and interacts with the magnetic field of the magnet so as to rotate the actuator arm around its pivot and thus positioning the transducer as desired.
The magnetic media disk or disks in the disk drive are mounted to a spindle. The spindle is attached to a spindle motor which rotates the spindle and the disks to provide read/write access to the various portions on the concentric tracks on the disks.
The actuator in the disk drive must be capable of a sufficient range of motion so that the transducer/slider combination attached to the suspension can access the maximum usable area of the disk surface to provide the most efficient use of the magnetic storage media and thus achieve the high data density desirable in data storage devices. Circumferential data tracks on the disk are written in a band extending radially from as far to the outer diameter of the disk (OD) as allowed by the necessity of keeping the entire slider over the disk and as far to the inner diameter of the disk (ID) as allowed without the slider or the suspension contacting the spindle on which the disk is mounted.
When the disk drive is not in operation, the disks are not rotating so that the air-bearing that supports the slider during operation is no longer provided. In the stopped condition, the slider rests in contact with the disk surface. When the disk drive is started, the slider stays in sliding contact with the disk surface until the disk achieves sufficiently high radial velocity to provide the air bearing that supports the slider in the operating condition. When the disk drive is shut down, the actuator locates the slider at the start/stop zone and then the spindle motor is turned off causing the disk or disks to stop rotating, resulting in the slider or sliders contacting the disk when the air-bearings can no longer support their load. The surface of the disks in the start/stop zone is usually specially textured to provide a low sticking and high durability interface, resulting in easy starting and low wear.
In the present art, a common practice reserves a radial band approximately the width of the slider at the ID of the available disk area for use as a start/stop zone. In normal operation, the actuator positions the transducer/slider/suspension combination radially with respect to the disk as described above. The inner and outer radial limits of the slider/suspension combination are established by mechanical limit stops which constrain the motion of the actuator positioning arm on which the suspension or suspensions are mounted. These limit stops are located near the rearward extensions of the actuator positioning arm. The ID limit stop limits actuator radial motion to define the innermost radius of the disk surface that can be accessed by the slider without danger of contact with the disk spindle. The OD limit stop limits actuator radial motion to define the outermost usable radius of the disk surface that can be accessed by the slider without danger of the slider running off the flat surface at the OD edge of the disk. The inner and outer radial limits of the slider/suspension combination with respect to the disk surface are required for safely restricting the radial position in case of drive electronics failure and to establish reference radii on the disk to provide information for recovery from a failure.
Because of the high density of data storage on the disks in a disk drive and to maximize the disk area available for user data, it is important to minimize the radial distance over the disk required to decelerate and stop the sliders during impact of the actuator with the limit stops. Equally important, the vibration of the slider/suspension combination induced by rapid deceleration of the actuator assembly on impact with the limit stops must be minimized to prevent damage to the slider or the disk caused by intermittent contacts. In the prior art, these requirements for effective limit stop design have been addressed and will be described briefly.
Many approaches to limit stop design exist in the prior art, all of which are directed to 1) keeping crash impact deflections as small as possible to maximize the disk area available for data storage and 2) keeping crash impact deceleration levels as low as possible to provide the highest possible margin for slider and/or disk damage from intermittent contacts.
A common approach is to completely form the limit stops of soft elastic or elastomeric materials to dissipate impact energy efficiently while limiting the impact deflections.
An alternative approach is to design the limit stops to include a spring or springs which can be suitably preloaded to more efficiently absorb the actuator impact energy resulting in smaller limit stop deflection to bring the actuator to rest. U.S. Pat. No. 5,455,726 issued to Liu describes a limit stop comprising a cantilever arrangement preloaded to improve dynamic energy absorption during crash stops. U.S. Pat. No. 5,369,538 issued to Moe et al. describes a limit stop comprising springs preloaded against reaction elements of the housing, the springs carrying stopping posts for the actuator arm. U.S. Pat. No. 4,796,131 issued to Chang describes a preloaded stop which includes a U-shaped spring mounted on a base plate.
The limit stops and materials used therein described in the prior art have several disadvantages which severely constrain their utility in practice. Elastomer or visco-elastic material parts generally have poor dimensional control and geometric precision requiring large tolerances which wastes valuable disk space. Dimensional stability of parts formed from these materials change with time, temperature and loading. Limit stops formed of these materials tend to adhere to the actuator when loaded against it for long periods (sticky limit stops). The materials generally have high outgassing characteristics leading to contamination of the disk drive components which can result in serious corrosion or stiction problems.
Limit stops that comprise preloaded spring arrangements are generally complex mechanical devices with many parts which adds to manufacturing complexity and cost. In addition, with many parts in the limit stop device, control of dimensional tolerances is much more difficult in the assembly of the limit stops in disk drives so that more disk space needs to be allocated for the limit stops.
It therefore can be seen that there is a need for a limit stop that can be fabricated with few parts and within well-defined mechanical tolerances, that minimizes impact deflections, limits impact deceleration levels, has good dimensional stability with time, temperature and loading, and has low outgassing characteristics.